Aflatoxin B1 (AFB1) is the most frequently encountered mycotoxin in hot and humid climates. Effects of AFB1 on animal performance and immunological variables have been an active area of research during the last 50 years. However, the impact of this mycotoxin on gastrointestinal tract has been generally overlooked. The aim of this thesis work was therefore to study the effects of in vitro and in vivo AFB1 exposure on electrophysiology of jejunal epithelium of chicken. To study the effects of in vitro exposure, segments from the middle jejunum of broilers were incubated in Ussing chambers in the presence of 0 to 3.75 [mikro]g AFB1/mL of buffer. Response of the jejunal epithelium to D-glucose (20 mmol/L) and carbamylcholine (200 [mikro]mol/L; analogue of acetylcholine and inducer of apical Cl- secretion) after incubation with AFB1 was also investigated. Addition of 3.75 [mikro]g of AFB1 caused an increase in short-circuit current (Isc) and transmural potential difference (Vt) between 12 to 27 min post-exposure as compared with the control. Glucose-induced [delta]Isc and percentage of [delta]Vt were reduced at 2.5 and 3.75 [mikro];g of AFB1/mL, respectively, as compared with the control. The carbamylcholine-induced [delta]Isc and [delta]Vt were both lower at 3.75 [mikro]g of AFB1/mL as compared with the control (-0.05 [mikro]A/cm2, 0.1 mV vs. 1.1 [mikro]A/cm2, and 0.6 mV, respectively). These observations indicate that in vitro exposure to AFB1 increases apical anion secretion in the jejunal epithelium of chicken. The negative effect of this increased anion secretion on active glucose uptake was however not prominent.
Based on the results of in vitro studies, a feeding trial (in vivo study) was conducted to investigate if similar results are seen after chronic exposure of broilers to AFB1. For this purpose, 7-d-old broilers were fed on either of three experimental diets i.e. no AFB1 diet, 0.07 mg AFB1/kg diet, and 0.75 AFB1 mg/kg diet. During 4th week of exposure, a linear decrease in the unit weight of small intestine was observed with increasing levels of AFB1. This reduction in unit weight progressed from proximal (duodenum) to distal (jejunum) small intestine with increase in the length of exposure. However, no AFB1-induced modulation of electrophysiological variables in jejunal epithelium could be noted.
Interestingly, a compensatory linear increase in the length of small intestine, resulting in nominal improvements in retention of macronutrients, was noted to occur during 4th week of exposure.
These data indicate that intestine of broilers may adapt to low levels of dietary AFB1 during a chronic exposure.